Shadow Slave (Shadow Master #2‪)‬

Felane, a warlock's apprentice, straddles the delicate line between tamer and tamed. When a slip of the tongue wounds her daemon lover's pride -- and solidifies Laen's growing fear of her power -- he punishes her, forcing her to service a troupe of underworld creatures to settle the debt. Felane welcomes this chance to mend the rift between them. No human -- nor any other daemon -- will ever satisfy her now she's had Laen.

But when his revenge goes to far, nearly killing her, restoring their trust in each other won't be easy. They must test their limits and probe the cracks in each other's boundaries -- or else their next time together may very well be their last.